Types of Artificial Hearts
Artificial hearts are devices that try to mimic either all or a part of the heart’s function. They are generally used for people who are not eligible for heart transplants. There are mainly two broad types of artificial hearts. There are Cardiac (heart) assist devices [CAD] and Total Artificial Hearts (TAH). CAD’s help the heart; they don’t do all the work for it. CAD’s are usually composed of left, right, or a combination of ventricular assist devices. When these devices are used the heart is not removed from the body, but rather the device takes the place of the heart’s components.
TAH’s are a little more complex in their nature. When these are used the heart must be completely removed from the body, and these devices are put in. these are similar to getting a human donor heart. TAH’s have decent reliability and are widely used in current times.
William Kolff in the early 1900’s invented the first TAH and from then on newer models were developed. The most widely known type of artificial heart is the Jarvik 7. This was invented by Dr. Robert Jarvik in 1982, so until relatively recently we had no replacement for a heart. The first patient it was used on ended up dying in only 112 days. The pump itself worked fine it was just its meeting with the body that caused problems. Currently Dr. Jarvik is working on a new type of artificial heart that is the size of one’s thumb. He will be calling this the Jarvik 2000.
A third type of artificial heart that is not yet been tested through time but has engineers rigorously working on is the electric heart. Dr. Michael DeBarkey has been the first to use this new device, but the public still has yet to see if it works well.
http://inventors.about.com/library/inventors/blartificialheart.htm
http://en.wikipedia.org/wiki/Artifical_heart
http://www.texasheart.org/Research/Devices/j7tah.cfm
Friday, July 18, 2008
The Jarvik-7 Artificial Heart
The Jarvik-7 Artificial Heart Among the most controversial of medical ethical issues is the Jarvik-7 Aritificial Heart. Its controversial nature began with its first permanent implantation in patient Barney Clark. Clark was a dentist from Seattle who wished to help further the research in this particular area. The issue in its entirety deals with the ethics of implanting humans with these hearts in this experimental manner.
Aside from its controversial nature and the media's subsequent focus on many of the complications in the patients that followed, the Jarvik-7 is the most successful artificial heart of its kind to have ever been designed. Five patients were implanted with the Jarvik-7 as a permanent replacement for the heart. On average, these patients lived 10 months, each with complications along the way. William Schroeder was among these five, and he lived longest on the Jarvik-7, for a period of 620 days.
Because the the Jarvik-7 proved to be viable for extended periods of time but not for "forever" so to speak, it has become part of the bridge process for the transplantation of a new heart. Patients who obtain and must live on Jarvik-7's during this bridge process have lived for years after receiving their donor hearts. For example, one patient lived fourteen years after receiving his donor heart.
The Jarvik-7 consists of two pumps that function in like the heart itself. It has two ventricles in the shape of a shpere and made of polyurethane. The pumps in the Jarvik-7 are powered by air pumps (pneumatic) that push the blood through inlet and outlet valves. The artificial heart itself is attached to the natural atria of the heart by Dacron felt. The powersource for the pumps themselves are powered by drive lines attached to an "air-driven, external power system" (Jarvik-7). The power system is a console roughly the size and weight of a home refrigerator, and is portable with a backup baterry system in case of power failure.
Aside from its controversial nature and the media's subsequent focus on many of the complications in the patients that followed, the Jarvik-7 is the most successful artificial heart of its kind to have ever been designed. Five patients were implanted with the Jarvik-7 as a permanent replacement for the heart. On average, these patients lived 10 months, each with complications along the way. William Schroeder was among these five, and he lived longest on the Jarvik-7, for a period of 620 days.
Because the the Jarvik-7 proved to be viable for extended periods of time but not for "forever" so to speak, it has become part of the bridge process for the transplantation of a new heart. Patients who obtain and must live on Jarvik-7's during this bridge process have lived for years after receiving their donor hearts. For example, one patient lived fourteen years after receiving his donor heart.
The Jarvik-7 consists of two pumps that function in like the heart itself. It has two ventricles in the shape of a shpere and made of polyurethane. The pumps in the Jarvik-7 are powered by air pumps (pneumatic) that push the blood through inlet and outlet valves. The artificial heart itself is attached to the natural atria of the heart by Dacron felt. The powersource for the pumps themselves are powered by drive lines attached to an "air-driven, external power system" (Jarvik-7). The power system is a console roughly the size and weight of a home refrigerator, and is portable with a backup baterry system in case of power failure.
- Robert Jarvik on the Jarvik-7. Jarvik Heart. <http://www.jarvikheart.com/basic.asp?id=69>.
- The Jarvik-7 Total Artificial Heart. April 2006. Texas Heart Institute. <http://www.texasheart.org/Research/Devices/j7tah.cfm>.
VAD's
When looking for a VAD, there are two categories to examine: Durability and bio-friendliness. The first category is pretty much self explanitory, asking 'how long does the machine normaly last' and 'can I expect mechanical failure,' but the second is a little broader. It asks 'what kind of medication do I need to take,' 'how much medication do I need to take', and 'does it increase my chance of infection.' Depending on what country you're in, you may also have to examine legal issues, as a number of devices are only approved in certain countries.
Based purely on longevity of a singal user, the best choice for a VAD is the Jarvik 2000, a very compact system which was able to support a patient for 7.5 years. However, it is still waiting approval in the U.S and has not of yet been used on a large number of patients. The Novacor LVAD, however, has been used on over 1,700 patiens, has approval in the US, EU and Japan, and, "among these recipients, 45 have been supported for more than two years, 24 for more than three years, 11 for more than four years and 1 for more than six years. Only 1.4% of the pumps have needed replacement. No patient deaths have been attributed to Novacor® LVAS failure." Sadly, both require anticoagulation medicine, but so do nearly all other VADs on the market. The exception to this is the Heartmate, which uses a biologically friendly material called fibrin to prevent the immune system from attacking the device. However, this too has disadvantages, as it increased the chances of infection and is not a durable as either the Jarvik or Novacor.
http://www.thoratec.com/medical-professionals/vad-product-information/heartmate-xve-lvad.aspx
http://en.wikipedia.org/wiki/Ventricular_assist_device
http://www.worldheart.com/products/novacor_lvas.cfm
http://www.jarvikheart.com/basic.asp?id=26
Based purely on longevity of a singal user, the best choice for a VAD is the Jarvik 2000, a very compact system which was able to support a patient for 7.5 years. However, it is still waiting approval in the U.S and has not of yet been used on a large number of patients. The Novacor LVAD, however, has been used on over 1,700 patiens, has approval in the US, EU and Japan, and, "among these recipients, 45 have been supported for more than two years, 24 for more than three years, 11 for more than four years and 1 for more than six years. Only 1.4% of the pumps have needed replacement. No patient deaths have been attributed to Novacor® LVAS failure." Sadly, both require anticoagulation medicine, but so do nearly all other VADs on the market. The exception to this is the Heartmate, which uses a biologically friendly material called fibrin to prevent the immune system from attacking the device. However, this too has disadvantages, as it increased the chances of infection and is not a durable as either the Jarvik or Novacor.
http://www.thoratec.com/medical-professionals/vad-product-information/heartmate-xve-lvad.aspx
http://en.wikipedia.org/wiki/Ventricular_assist_device
http://www.worldheart.com/products/novacor_lvas.cfm
http://www.jarvikheart.com/basic.asp?id=26
Valve Replacements
· Ball and Cage - The caged ball design is one of the early mechanical heart valves that use a small ball that is held in place by a welded metal cage. The ball in cage design was modeled after ball valves used in industry to limit the flow of fluids to a single direction. Natural heart valves allow blood to flow straight through the center of the valve. This property is known as central flow, which keeps the amount of work done by the heart to a minimum. With non-central flow, the heart must work harder to compensate for the momentum lost to the change of direction of the fluid. Caged-ball valves completely block central flow, therefore the blood requires more energy to flow around the central ball. In addition, the ball is notorious for causing damage to blood cells due to collisions. Damaged blood cells release blood clotting ingredients; hence the patients are required to take lifelong prescriptions of anticoagulants.
· Sinlge Leaflet - tilting disc to better mimic the natural patterns of blood flow. The tilting-disc valves have a polymer disc held in place by two welded struts. The disc floats between the two struts in such a way, as to close when the blood begins to travel backward and then reopens when blood begins to travel forward again. The tilting-disc valves are vastly superior to the ball-cage design. The titling-disc valves open at an angle of 60° and close shut completely at a rate of 70 times/minute. This tilting pattern provides improved central flow while still preventing backflow. The tilting-disc valves reduce mechanical damage to blood cells. This improved flow pattern reduced blood clotting and infection. However, the only problem with this design is its tendency for the outlet struts to fracture as a result of fatigue from the repeated ramming of the struts by the disc.
· BiLeaflet - two semicircular leaflets that pivot on hinges. The carbon leaflets exhibit high strength and excellent biocompatibility. The leaflets swing open completely, parallel to the direction of the blood flow. They do not close completely, which allows some backflow. Since backflow is one of the properties of defective valves, the bileaflet valves are still not ideal valves. The bileaflet valve constitutes the majority of modern valve designs. These valves are distinguished mainly for providing the closest approximation to central flow achieved in a natural heart valve.
· Animal Tissue Valves (porcine/bovine) - Both the porcine and bovine pericardial valves are stented valves. The metal stent in these valves takes up room which could be available for blood flow. Stentless valves are made by removing the entire aortic root and adjacent aorta as a block, usually from a pig. The coronary arteries are tied off, and the entire section is trimmed and then implanted into the patient. The St. Jude Toronto Stentless Porcine Valve (SPV) is one such valve. It appears to have excellent hemodynamics, and a significant decrease in the thickness of the heart has been observed after the valve is implanted. However, the valve is extremely difficult to implant, and it is still too new to have any valid data accounting for durability. The most common cause of bioprosthesis failure is stiffening of the tissue due to the build up calcium. Calcification can cause a restriction of blood flow through the valve (stenosis) or cause tears in the valve leaflets. Since younger patients have a greater calcium metabolism, bioprostheses tend to last best in senior citizens.
· Homograft - a valve that is transplanted from a deceased person to a recipient. A recipient has minimal problems with valve rejection and they do not require immunosuppressive therapy. A homograft that has been donated must be cryopreserved in liquid nitrogen until it is needed. In cases where the valve implants fit the dimensions of the patient correctly, homografts tend to have good hemodynamics and good durability. However, it is not clear whether homografts have better hemodynamics or durability than animal tissue valves.
· Autograft – The dysfunctional aortic valve is removed and the patient's pulmonic valve is then transplanted to the aortic position. A homograft pulmonic valve is usually used to replace the patient’s pulmonic valve. The Ross procedure allows the patient the advantage of receiving a living valve in the aortic position.. The tissues of the patients’ pulmonary valve have not shown a tendency to calcify, degenerate, perforate, or develop leakage.
I think the Pulmonary Autograft is the most effective type of valve replacement. It seems to last the longest with the least complications. The long term survival and freedom from complications for patients with aortic valve disease are better with the Ross Procedure than any other type of valve replacement. After 20 years, only 15% of patients require additional valve procedures. In cases where a human pulmonary artery homograft is used to replace the patients’ pulmonary valve, freedom from failure has been 94% after 5 years time, and 83% at 20 years. This procedure proves at the moment to be very successful.
http://cape.uwaterloo.ca/che100projects/heart/files/testing.htm#mech1
· Sinlge Leaflet - tilting disc to better mimic the natural patterns of blood flow. The tilting-disc valves have a polymer disc held in place by two welded struts. The disc floats between the two struts in such a way, as to close when the blood begins to travel backward and then reopens when blood begins to travel forward again. The tilting-disc valves are vastly superior to the ball-cage design. The titling-disc valves open at an angle of 60° and close shut completely at a rate of 70 times/minute. This tilting pattern provides improved central flow while still preventing backflow. The tilting-disc valves reduce mechanical damage to blood cells. This improved flow pattern reduced blood clotting and infection. However, the only problem with this design is its tendency for the outlet struts to fracture as a result of fatigue from the repeated ramming of the struts by the disc.
· BiLeaflet - two semicircular leaflets that pivot on hinges. The carbon leaflets exhibit high strength and excellent biocompatibility. The leaflets swing open completely, parallel to the direction of the blood flow. They do not close completely, which allows some backflow. Since backflow is one of the properties of defective valves, the bileaflet valves are still not ideal valves. The bileaflet valve constitutes the majority of modern valve designs. These valves are distinguished mainly for providing the closest approximation to central flow achieved in a natural heart valve.
· Animal Tissue Valves (porcine/bovine) - Both the porcine and bovine pericardial valves are stented valves. The metal stent in these valves takes up room which could be available for blood flow. Stentless valves are made by removing the entire aortic root and adjacent aorta as a block, usually from a pig. The coronary arteries are tied off, and the entire section is trimmed and then implanted into the patient. The St. Jude Toronto Stentless Porcine Valve (SPV) is one such valve. It appears to have excellent hemodynamics, and a significant decrease in the thickness of the heart has been observed after the valve is implanted. However, the valve is extremely difficult to implant, and it is still too new to have any valid data accounting for durability. The most common cause of bioprosthesis failure is stiffening of the tissue due to the build up calcium. Calcification can cause a restriction of blood flow through the valve (stenosis) or cause tears in the valve leaflets. Since younger patients have a greater calcium metabolism, bioprostheses tend to last best in senior citizens.
· Homograft - a valve that is transplanted from a deceased person to a recipient. A recipient has minimal problems with valve rejection and they do not require immunosuppressive therapy. A homograft that has been donated must be cryopreserved in liquid nitrogen until it is needed. In cases where the valve implants fit the dimensions of the patient correctly, homografts tend to have good hemodynamics and good durability. However, it is not clear whether homografts have better hemodynamics or durability than animal tissue valves.
· Autograft – The dysfunctional aortic valve is removed and the patient's pulmonic valve is then transplanted to the aortic position. A homograft pulmonic valve is usually used to replace the patient’s pulmonic valve. The Ross procedure allows the patient the advantage of receiving a living valve in the aortic position.. The tissues of the patients’ pulmonary valve have not shown a tendency to calcify, degenerate, perforate, or develop leakage.
I think the Pulmonary Autograft is the most effective type of valve replacement. It seems to last the longest with the least complications. The long term survival and freedom from complications for patients with aortic valve disease are better with the Ross Procedure than any other type of valve replacement. After 20 years, only 15% of patients require additional valve procedures. In cases where a human pulmonary artery homograft is used to replace the patients’ pulmonary valve, freedom from failure has been 94% after 5 years time, and 83% at 20 years. This procedure proves at the moment to be very successful.
http://cape.uwaterloo.ca/che100projects/heart/files/testing.htm#mech1
Shanice
VADs can be used to take over the right ventricle, the left ventricle and in some cases it is used to take over both ventricles. There are two types of pumps used in a VAD. First there is a pulsatile pump, which pumps blood through the body with a normal pulsing action then there is are centrifugal pumps that just sent the blood throughout the body continuously without a pulse. The centrifugal pump is recognized as the second generation of pumps because they are simpler than the pulsatile pump and it is smaller and more reliable.
Bioprosthetic Valves
-Bioprosthetic Valves are heart valves taken from either a human or an animal and used as a prosthetic.
-Theses Bioprosthetic valves are much more advantageous than artificial valves not only because they eliminate the need for long-term anti-coagulants, but they also don't cause any harm to blood cells.
- The human valves are separated into two categories homografts, which replace a human's valve with another human's valve, and autographs, which simply repositions a valve which is already in the patients body.
-Homografts have little to no problems with another human being able to accept the foreign valve, have good hemodynamics, which is simply defined as how much resistance to blood flow the valve gives, and durability.
-The most common procedure that uses autographs is called the Ross Procedure which replaces the valve in the aortic valve with the one in the pulmonic valve. The Ross Procedure is so effective that after 20 years only 15 percent of patients needed another surgery.
-This chart shows how successful the Homograft surgeries have been. The Blue Bar is the Percent Survival Rate, the Purple bar is percent of patients without Endocarditis, the yellow bar shows percent without pulminary tissue failure, and the green bar shows the percent of people who didn't need another surgery.
Websites
Artificial Pacemakers
An Artificial Pacemaker is a device that helps control irregular heart rhythms. Irregular in this case meaning, a heart that beats too slow, too fast, or just doesn’t beat in a regular fashion. The pacemaker device is usually implanted in the chest or abdomen. The name for irregular heart rhythms is arrhythmia. There are also 4 different methods to pacing an abnormally beating heart.
1. Percussive Pacing
2. Transcutaneous Pacing
3. Transvenous Pacing
4. Permanent Pacing
Out of all of these methods of pacing only the fourth method is permanent. The rest of the pacemakers are simply there to provide a bridge to the Permanent Pacing. The first two methods are a short bridge to Permanent Pacing while the third, Transvenous Pacing can be removed later without the addition of Permanent Pacing if the heart recovers from its arrhythmia. The Permanent Pacing device is usually made out of titanium since it is relatively inert inside the human body. The battery is usually a Lithium battery that has to be replaced about every fifteen years or so. If I had to choose which Pacemaker is the best I would say Permanent Pacing is the best. The only reason is because the permanent option is the only option that will last for any considerable amount of time.
http://en.wikipedia.org/wiki/Pacemakers#Methods_of_pacing
http://www.nhlbi.nih.gov/health/dci/Diseases/pace/pace_whatis.html
Biological Heart Valves
The heart has four chambers and blood is pumped throughout these chambers with help from heart valves. Normally, these valves open fully to let blood flow in only one direction and then close completely. However, due to heart defects, infections, or rheumatic fever, a valve can become damaged and fail to open or close fully. One way of treatment is replacing the valve with one of two types of artificial valves, mechanical or biological.
Biological valves come from different animals and are a lot more similar to human valves than mechanical. The two different types of biological valves include an implantation of a porcine valve or the use of biological tissue to create new leaflets for the valve. The porcine (or pig) valve is very similar to human valves and is the best fit for a human heart. This full implantation is known as xenograft or the "transplant from one species to another". However this is not the best form of biological valve replacement because the body tends to reject the replacement as foreign material and medication does not always help. The second type of biological valve replacement is usually more successful and more reliable. This type uses biological tissue usually of bovine (cows) or equine (horses) to make new cusps that are sewn into a metal frame. This is very effective because the tissue is strong, flexible, and durable. It is also sterilized to minimize the rejection from the body's immune system. Also, unlike the mechanical valves, the patient is not required to stay on blood thinners or take anticoagulation therapy making it the best recommendation.
http://www.americanheart.org/presenter.jhtml?identifier=4598
http://en.wikipedia.org/wiki/Artificial_heart_valve
Ventricular Assist Devices
Ventricular assist devices come in three varieties, Left Ventricular Assist Device (LVAD), Right Ventricular Assist Device (RVAD), and Bi Ventricular Assist Device (BiVAD). Although all of them affect different parts of the heart., they all share the same goal, and that is to extend the life of a person either for a short period of time "destination therapy" or until a better solution can be found "bridge therapy." VAD's in general vary largely in design but most are implanted in a similar fashion. This method of insertion being the insertion of tubing into the affected ventricle(s) that leads to a pump which pumps the blood from the ventricle(s) to the outgoing vessel ie. the pulmonary artery, aorta, or both. Where VAD’s largely differ is in the pump design.
There are two main types of pumps when it comes to VAD’s, these two being pulsatile pumps and continuous flow pumps. Pulsatile pumps rely on some form of pneumatic device to push the blood along the blood vessels. This requires that there be an opening to an air source ( a tube leading from the displacement pump to the outer body). The other major type of pump, continuous flow pumps, utilizes continuous flow as the mechanism of blood transport. This is achieved by a rotary “centrifugal” pump, many continuous flow pumps are still very controversial both in their method or action and their implantation. There is a lot of controversy on how one should suspend the rotary mechanism, to do little damage to the blood and surrounding structure, another issue is the fact that there is little known about how the body deals with continued flow.
VAD’s are implanted into the body for bridge therapy and destination therapy, but how well do they achieve this? In one study it was shown that people who were on a VAD prior to heart transplant had a 40% better chance of survival without any complications as opposed to those on alternative treatments. 1VAD’s are meant for short term use, but what if they were used for long term, about how long can you expect them to last? One could usually expect a longer life, as compared to those on medical treatment. According to one study you have a 15% better chance of surviving for 2+ years on a VAD than on medication.1 Complications arise, as do with any type of major procedure, among possible problems, the largest causes of death are mechanical failure and infection. Being a machine, VAD’s can’t last forever, and they don’t, usually suffering some form of mechanical failure within the first 2 years. Disease is another factor, whether caused by surgery itself or assisted by the hospitable growing area that the VAD and components provide, it is a problem that causes many deaths related to VAD’s.
1: "Ventricular assist device." Wikipedia, The Free Encyclopedia. 19 Jun 2008, 02:04 UTC. Wikimedia Foundation, Inc. 18 Jul 2008 <http://en.wikipedia.org/w/index.php?title=Ventricular_assist_device&oldid=220274111>.
VAD Pump Designs
VADs, or ventricular assist devices, are used when needed to aid the hardest-working parts of the heart - the ventricles. Most of these are continuously flowing, meaning they don't stop and start moving blood in a similar pattern to a functional heart. Continuous flow VADs haven't shown any life-threatening side effects related to the unnatural flow of blood, and they are easier to make. They are most often used in the right ventricle, the only left ventricular assist devices (in the US) being pulsatile, mimicing the heart's natural beating.
The motors in the continuous flow VADs contain magnets with coils around them. Electrical currents are sent through the coils at controlled levels to spin the magnet, which is connected to the rest of he assembly, which therefore moves blood. Continuous flow pumps use either axial or centrifugal pumps. Axial pumps have helix-shaped blades which spin to act much like a propeller on a boat, propelling the blood along the motor's axis, while cenrifugal pumps have rotors shaped to spin the blood toarwds the outer edges of the pump. All of the pumps certified for use in the US by the FDA use bearings to hold the rotor in place; however, there are pumps used in European countries that use magnetic or hydrodynamic forces to suspend the rotor. The benefit of these newer forms of suspension is that there is much less wear on the pump with the lack of bearings (less moving parts), and also less wear on the blood.
The design I think is the best is the axial pump with an electromagnetically suspended rotor. I feel that a centrifugal pump would be more stressful on the blood than an axial pump, and also less efficient; an axial pump pushes the blood in one direction, while the the centrifugal pump does this by spinning the blood around a lot first. Also, the electromagnetically suspended rotor seems a better choice simply due to the reduced wear on the device, making it more reliable.
http://en.wikipedia.org/wiki/Ventricular_assist_device
The motors in the continuous flow VADs contain magnets with coils around them. Electrical currents are sent through the coils at controlled levels to spin the magnet, which is connected to the rest of he assembly, which therefore moves blood. Continuous flow pumps use either axial or centrifugal pumps. Axial pumps have helix-shaped blades which spin to act much like a propeller on a boat, propelling the blood along the motor's axis, while cenrifugal pumps have rotors shaped to spin the blood toarwds the outer edges of the pump. All of the pumps certified for use in the US by the FDA use bearings to hold the rotor in place; however, there are pumps used in European countries that use magnetic or hydrodynamic forces to suspend the rotor. The benefit of these newer forms of suspension is that there is much less wear on the pump with the lack of bearings (less moving parts), and also less wear on the blood.
The design I think is the best is the axial pump with an electromagnetically suspended rotor. I feel that a centrifugal pump would be more stressful on the blood than an axial pump, and also less efficient; an axial pump pushes the blood in one direction, while the the centrifugal pump does this by spinning the blood around a lot first. Also, the electromagnetically suspended rotor seems a better choice simply due to the reduced wear on the device, making it more reliable.
http://en.wikipedia.org/wiki/Ventricular_assist_device
Prosthetic Heart Valves
A major problem that scientists and engineers have researched to fix is a diseased or dysfunctional heart valve. Prosthetic heart valves have been engineered in order to replace the valves. If a heart valve malfunctions, the entire circulatory system could be affected. When a valve is not working properly, it tends to allow some blood to flow backwards, which decreases the amount of oxygen that is delivered throughout the body with each heart beat. Another valve malfunction is known as a stenotic valve. When a valve is considered stenotic it is stiff and thus does not open fully which forces the heart to pump more to move the blood through the small opening.
There are two major types of prosthetic heart valves: mechanical heart valves and biological heart valves. A mechanical valve is synthetically made and generally is capable of lasting a lifetime because the materials are non-corrosive. Biological valves, on the other hand, are heart valves of human cadavers or certain animals. The biological valves must be sterilized properly for human implantation for the body to better accept the foreign substance. The available products that are being used to replaced dysfunctional valves vary from mechanical leaflet valves to porcine valves that come from pigs.
One particular valve consists of two leaflet, or flap-like, structures made of carbon that are in the shape of a circle. The circle is surrounded by a polyester fabric. Such a valve is used to replace an aortic or mitral valve. The patients of mechanical valves, however, usually must be able to tolerate anticoagulant drugs to prevent blood clotting on the synthetic valve. Another mechanical heart can be created with two half-discs covered by a fabric ring. The discs are made of graphite, tungsten, and carbon coating so that they will not corrode.
A biological valve can be made from part of a cow’s jugular vein that is sterilized. The vein is treated with preservatives to keep it both durable and flexible. The cow’s vein has three leaflets that open to allow the blood flow. Another biological valve can use a pig’s aortic valve that is treated with preservatives and sterilized. Some of the pig valves cannot be used in patients with high calcium metabolism, as the valve will deteriorate rather quickly. Some of the bovine, or cow, and porcine, or pig, valves are contained within a plastic stent which is attached to the walls of the heart; therefore the valve is a mixture of both mechanical and biological.
After looking at the majority of the prosthetic valves that are available today, it appears that it is better to choose a mechanical valve. In the implantation of a mechanical valve, the body is less likely to reject the valve, even though anticoagulants are generally needed. Mechanical valves can also last much longer than most biological valves.
http://www.fda.gov/hearthealth/treatments/medicaldevices/prostheticheartvalve.html
http://encarta.msn.com/encyclopedia_761572608_4/Heart.html#p67
There are two major types of prosthetic heart valves: mechanical heart valves and biological heart valves. A mechanical valve is synthetically made and generally is capable of lasting a lifetime because the materials are non-corrosive. Biological valves, on the other hand, are heart valves of human cadavers or certain animals. The biological valves must be sterilized properly for human implantation for the body to better accept the foreign substance. The available products that are being used to replaced dysfunctional valves vary from mechanical leaflet valves to porcine valves that come from pigs.
One particular valve consists of two leaflet, or flap-like, structures made of carbon that are in the shape of a circle. The circle is surrounded by a polyester fabric. Such a valve is used to replace an aortic or mitral valve. The patients of mechanical valves, however, usually must be able to tolerate anticoagulant drugs to prevent blood clotting on the synthetic valve. Another mechanical heart can be created with two half-discs covered by a fabric ring. The discs are made of graphite, tungsten, and carbon coating so that they will not corrode.
A biological valve can be made from part of a cow’s jugular vein that is sterilized. The vein is treated with preservatives to keep it both durable and flexible. The cow’s vein has three leaflets that open to allow the blood flow. Another biological valve can use a pig’s aortic valve that is treated with preservatives and sterilized. Some of the pig valves cannot be used in patients with high calcium metabolism, as the valve will deteriorate rather quickly. Some of the bovine, or cow, and porcine, or pig, valves are contained within a plastic stent which is attached to the walls of the heart; therefore the valve is a mixture of both mechanical and biological.
After looking at the majority of the prosthetic valves that are available today, it appears that it is better to choose a mechanical valve. In the implantation of a mechanical valve, the body is less likely to reject the valve, even though anticoagulants are generally needed. Mechanical valves can also last much longer than most biological valves.
http://www.fda.gov/hearthealth/treatments/medicaldevices/prostheticheartvalve.html
http://encarta.msn.com/encyclopedia_761572608_4/Heart.html#p67
The Three Types of Stents
Jason Sedlak
July 17th :Types of Stents
A stent is a mesh-wire tube placed inside a passageway in the body to prevent that path from constricting or closing off. While the most known placement is in coronary arteries, stents can be put in to improve flow to various organs and even to prop open the esophagus. The most basic stent is simply metal, although newer stents are features such as releasing the anticoagulants the patient normally has to take directly into the blood.
There are three major types of stents:
BMSs (Bare metal stents)
DESs (Drug-eluting stents)
and “Covered stents”
Out of these three types, I would recommend the DES. While the covered stent prevents tissue from growing through the meshing (This type of stent has a layer of non-toxic metal alloy surrounding it) and allows blood flow to resume at a pretty normal rate, it is bulkier, harder to place, and is not able to fit into more restricted areas. If I needed stents, I would go with the drug-releasing smaller stent; it just seems easier to incorporate despite the promising potential of the covered stent.
http://www.research.ucla.edu/tech/ucla05-177.htm
http://en.wikipedia.org/wiki/Stents#Types_of_stent
Left Ventricular Assist Devices
Marissa Reitsma
7/17/08
Left Ventricular Assist Devices
There are at least five approved LVAD devices approved for use in the United States. The Incor device, manufactured by the Berlin Heart Company, is certified and manufactured for use in the European Union. Also, there are more than four devices currently in clinical trial stage and awaiting FDA approval. The devices in the trial stage have focused on improving the lifespan of LVAD devices. Many of the newer devices, including the Jarvik 2000, serve as supplement supports to the left ventricle’s naturally pumping which allows the patient to eventually build up strength in order to become independent of the device.
Each of the current LVAD options boasts its strengths, yet it also has inevitable weaknesses. Although the Heartmate, developed by Thoratec, is used in roughly four out of five transplants, the Jarvik 2000 has some promising features that make it stand out. The Jarvik device is much smaller and lighter (it is only a twentieth to a tenth of its competitors size) than much of its competition, and the implant can fit inside the left ventricle. It also has only one moving part, no valves, and since it sits within the natural heart, it has no inflow or outflow valves, which reduces the risk of failure. Contrary to its bulkier competition, the Jarvik LVAD is totally silent. The Jarvik implant has a very user friendly interface because it is manually programmable. As long as the patient is informed and competent, many sources sugest that this is more effective than a computer run device. Finally, the battery life of the implant is eight to ten hours, allowing the patient more freedom.
Works Consulted
http://en.wikipedia.org/wiki/Ventricular_assist_device
http://www.jarvikheart.com/basic.asp?id=19
http://www.worldheart.com/products/novacor_lvas.cfm
http://www.thoratec.com/medical-professionals/vad-product-information/heartmate-ll-lvad.aspx
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